While conducting biological tests, it is often necessary to dispense liquids, such as reagents, onto test slides containing tissue specimens. When analyzing tumor tissue for example, a thinly sliced section of the tissue might be placed on a slide and processed through a variety of steps, including dispensing predetermined amounts of liquid reagents onto the tissue. Automated reagent fluid dispensing devices have been developed to precisely apply a sequence of preselected reagents to test slides.
One example of a known reagent dispensing system is illustrated in U.S. Pat. No. 5,232,664 to Krawzak et al. In that system, a reagent dispensing tray can receive plural reagent containers and may include a means for positioning selected reagent containers over slides to receive reagent. An air cylinder or equivalent actuator makes contact with an individual cartridge effecting movement of a spring loaded displacement member. The spring loaded displacement member slides within a cylinder thereby reducing the reagent volume in the cylinder, which in turn causes reagent fluid to be applied over the slides.
One disadvantage associated with such systems is that the dispensing systems often utilize a sliding plunger that is in sealing contact with an internal surface of a cylinder. As a result, the useful life of such systems is limited by wear between the plunger and the cylinder. Systems that include a sliding plunger and cylinder configuration also require precise fitting of the plunger seal so that a fluid seal is maintained between the sliding surfaces during changes in direction of the plunger displacement. In view of these disadvantages, there exists a need for a reagent dispensing system that does not rely upon a sliding seal between a plunger and a cylinder.
An additional disadvantage associated with conventional reagent dispensing systems is the potential misalignment of individual cartridges within mounting apertures of a mounting assembly. In view of this disadvantage, there exists a need for a reagent dispensing system including cartridges that are shaped so as to self-align within similarly-shaped mounting apertures.